Table 1.
Characteristics of breast cancer patients in the WECARE I and II Study
| Characteristics | CBC cases | UBC controls |
|---|---|---|
| N (%) | N (%) | |
| Overall numbers | 1521 (100) | 2212 (100) |
| Study area | ||
| Iowaa | 201(13) | 314 (14) |
| Seattleb | 224 (15) | 317 (14) |
| Ontarioc | 159 (10) | 157 (7) |
| Californiad | 658 (43) | 967 (44) |
| Denmarke | 279 (18) | 457 (21) |
| Age at first breast cancer (years) | ||
| ≤39 | 268 (18) | 384 (17) |
| 40–49 | 808 (53) | 1180 (53) |
| 50–54 | 445 (29) | 648 (29) |
| Age at CBC/reference date (years) | ||
| ≤39 | 100 (6) | 147 (7) |
| 40–49 | 446 (29) | 691 (31) |
| 50–59 | 719 (48) | 1087 (49) |
| ≥60 | 256 (17) | 287 (13) |
| Year of diagnosis of first breast cancer | ||
| 1985–1989 | 303 (20) | 580 (26) |
| 1990–1994 | 572 (38) | 871 (39) |
| 1995–1999 | 426 (28) | 551 (25) |
| 2000–2004 | 186 (12) | 190 (9) |
| 2005–2008 | 34 (2) | 20 (1) |
| Time since first breast cancer (years) | ||
| 1–4 | 586 (39) | 986 (45) |
| 5–9 | 574 (38) | 804 (36) |
| ≥10 | 361 (24) | 422 (19) |
| First-degree family history of breast cancer | ||
| Yes | 497 (33) | 466 (21) |
| No | 1004 (66) | 1706 (77) |
| Unknown | 20 (1) | 40 (2) |
| Lobular histology of first breast cancer | ||
| Yes | 179 (12) | 223 (10) |
| No | 1342 (88) | 1989 (90) |
| Stage of first breast cancer | ||
| Local | 1061 (70) | 1442 (65) |
| Regional | 448 (29) | 759 (34) |
| Unknown | 12 (1) | 11 (1) |
| ER/PR status of the first breast cancer | ||
| Positive | 863 (57) | 1379 (62) |
| Negative | 413 (27) | 473 (21) |
| Unknown | 245 (16) | 360 (16) |
| Radiation for first breast cancerf | ||
| Yes | 880 (58) | 1686 (76) |
| No | 641 (42) | 525 (24) |
| Chemotherapy for first breast cancer | ||
| Yes | 822 (54) | 1289 (58) |
| No | 699 (46) | 923 (42) |
| Tamoxifen use for first breast cancer | ||
| Yes | 467 (31) | 787 (36) |
| No | 1054 (69) | 1425 (64) |
| Other endocrine therapy for first breast cancerg | ||
| Yes | 89 (6) | 141 (6) |
| No | 1432 (94) | 2071 (94) |
aThe State Health Registry of Iowa
bCancer Surveillance System of the Fred Hutchinson Cancer Research Center
cThe Ontario Cancer Registry
dFour study centers: 1) Los Angeles County Cancer Surveillance Program, 2) The Cancer Surveillance Program of Orange County/San Diego-Imperial Organization for Cancer Control, 3) Greater Bay Area Cancer Registry (San Francisco Bay Area Region and Santa Clara Region), and 4) Sacramento and Sierra Center Registry (Sacramento Region)
eThe Danish Breast Cancer Cooperative Group Database supplemented by the Danish Cancer Registry
fRadiation for first breast cancer was unknown for one control
gAromatase inhibitors (67 cases and 99 controls) and other anti-estrogens
CBC contralateral breast cancer, ER/PR estrogen receptor/progesterone receptor (if either ER or PR was positive, we considered the ER/PR status as positive), UBC unilateral breast cancer